Devices within close proximity of each other may wirelessly transfer energy for various reasons. For instance, a device may wirelessly charge another device's battery. Also, a device may wirelessly provide another device with operational power. Such exchanges of energy are called wireless power transfer (WPT). Further, two devices may exchange wireless signals to engage in near field communications (NFC).
Such wireless energy transfer may involve an electromagnetic coupling between proximate coils. For example, a first device may have a transmitting coil and a second device may have a receiving coil. When an electrical current flows through the transmitting coil, a magnetic field is generated. In turn, this magnetic field may induce an electrical current in the receiving coil.
It is desirable for coil structures to efficiently transfer wireless energy. Further, it is desirable for such structures to be integrated into multiple host devices without significant modification or customization. Moreover, it is desirable for such structures to be resistant to noise and interference, as well as to provide energy transfer at various spatial directions.